Keeping track of descendants that draw content instead of recalcualting

cc/layers/image_layer.cc

Index: cc/layers/image_layer.cc
diff --git a/cc/layers/image_layer.cc b/cc/layers/image_layer.cc
index cada84df3ccb4a0ce63731db532f2e0cd1f08358..de3fad0d0f6123c0511910ecc543faef1b444b2f 100644
--- a/cc/layers/image_layer.cc
+++ b/cc/layers/image_layer.cc
@@ -30,9 +30,14 @@ void ImageLayer::SetBitmap(const SkBitmap& bitmap) {
     return;
 
   bitmap_ = bitmap;
+  UpdateDrawsContent(HasDrawableContent());
   SetNeedsDisplay();
 }
 
+bool ImageLayer::HasDrawableContent() const {
+  return !bitmap_.isNull() && TiledLayer::HasDrawableContent();
+}
+
 void ImageLayer::SetTexturePriorities(const PriorityCalculator& priority_calc) {
   // Update the tile data before creating all the layer's tiles.
   UpdateTileSizeAndTilingOption();
@@ -77,10 +82,6 @@ void ImageLayer::CalculateContentsScale(float ideal_contents_scale,
   *content_bounds = gfx::Size(bitmap_.width(), bitmap_.height());
 }
 
-bool ImageLayer::DrawsContent() const {
-  return !bitmap_.isNull() && TiledLayer::DrawsContent();
-}
-
 void ImageLayer::OnOutputSurfaceCreated() {
   SetTextureFormat(
       layer_tree_host()->GetRendererCapabilities().best_texture_format);